Include classification label in project API

This attribute was not exposed in the API, while it should have
been. The attribute is hidden when the feature is not available for
the project.

ee/changelogs/unreleased/bvl-include-classification-label-in-projects-api.yml

+---
+title: Include classification label in project API
+merge_request: 8426
+author:
+type: fixed

ee/lib/ee/api/entities.rb

@@ -23,6 +23,8 @@ module EE
           expose :mirror_trigger_builds, if: ->(project, _) { project.mirror? }
           expose :only_mirror_protected_branches, if: ->(project, _) { project.mirror? }
           expose :mirror_overwrites_diverged_branches, if: ->(project, _) { project.mirror? }
+          expose :external_authorization_classification_label,
+                 if: ->(project, _) { project.feature_available?(:external_authorization_service) }
         end
       end
 

ee/spec/requests/api/projects_spec.rb

@@ -257,4 +257,52 @@ describe API::Projects do
       end
     end
   end
+
+  describe 'GET /projects/:id' do
+    context 'with external authorization' do
+      let(:project) do
+        create(:project,
+               namespace: user.namespace,
+               external_authorization_classification_label: 'the-label')
+      end
+
+      context 'when the user has access to the project' do
+        before do
+          external_service_allow_access(user, project)
+        end
+
+        it 'includes the label in the response' do
+          get api("/projects/#{project.id}", user)
+
+          expect(response).to have_gitlab_http_status(200)
+          expect(json_response['external_authorization_classification_label']).to eq('the-label')
+        end
+      end
+
+      context 'when the external service denies access' do
+        before do
+          external_service_deny_access(user, project)
+        end
+
+        it 'returns a 404' do
+          get api("/projects/#{project.id}", user)
+
+          expect(response).to have_gitlab_http_status(404)
+        end
+      end
+
+      context 'it does not return the label when the feature is not available' do
+        before do
+          stub_licensed_features(external_authorization_service: false)
+        end
+
+        it 'does not include the label in the response' do
+          get api("/projects/#{project.id}", user)
+
+          expect(response).to have_gitlab_http_status(200)
+          expect(json_response['external_authorization_classification_label']).to be_nil
+        end
+      end
+    end
+  end
 end